One known type of information storage device is a disk drive device that uses magnetic media to store data and a movable read/write head that is positioned over the media to selectively read from or write to the disk.
Consumers are constantly desiring greater storage capacity for such disk drive devices, as well as faster and more accurate reading and writing operations. Thus, disk drive manufacturers have continued to develop higher capacity disk drives by, for example, increasing the density of the information tracks on the disks by using a narrower track width and/or a narrower track pitch. However, each increase in track density requires that the disk drive device have a corresponding increase in the positional control of the read/write head in order to enable quick and accurate reading and writing operations using the higher density disks. As track density increases, it becomes more and more difficult using known technology to quickly and accurately position the read/write head over the desired information tracks on the storage media. Thus, disk drive manufacturers are constantly seeking ways to improve the positional control of the read/write head in order to take advantage of the continual increases in track density.
One approach that has been effectively used by disk drive manufacturers to improve the positional control of read/write heads for higher density disks is to employ a secondary actuator, known as a micro-actuator, that works in conjunction with a primary actuator to enable quick and accurate positional control for the read/write head. Disk drives that incorporate a micro-actuator are known as dual-stage actuator systems.
Various dual-stage actuator systems have been developed in the past for the purpose of increasing the access speed and fine tuning the position of the read/write head over the desired tracks on high density storage media. Such dual-stage actuator systems typically include a primary voice-coil motor (VCM) actuator and a secondary micro-actuator, such as a PZT element micro-actuator. The VCM actuator is controlled by a servo control system that rotates the actuator arm that supports the read/write head to position the read/write head over the desired information track on the storage media. The PZT element micro-actuator is used in conjunction with the VCM actuator for the purpose of increasing the positioning access speed and fine tuning the exact position of the read/write head over the desired track. Thus, the VCM actuator makes larger adjustments to the position of the read/write head, while the PZT element micro-actuator makes smaller adjustments that fine tune the position of the read/write head relative to the storage media. In conjunction, the VCM actuator and the PZT element micro-actuator enable information to be efficiently and accurately written to and read from high density storage media.
One known type of micro-actuator incorporates PZT elements for causing fine positional adjustments of the read/write head. Such PZT micro-actuators include associated electronics that are operable to excite the PZT elements on the micro-actuator to selectively cause expansion or contraction thereof. The PZT micro-actuator is configured such that expansion or contraction of the PZT elements causes movement of the micro-actuator which, in turn, causes movement of the read/write head. This movement is used to make faster and finer adjustments to the position of the read/write head, as compared to a disk drive unit that uses only a VCM actuator. Exemplary PZT micro-actuators are disclosed in, for example, JP 2002-133803, entitled “Micro-actuator and HGA” and JP 2002-074871, entitled “Head Gimbal Assembly Equipped with Actuator for Fine Position, Disk Drive Equipped with Head Gimbals Assembly, and Manufacture Method for Head Gimbal Assembly.”
FIG. 1 illustrates a conventional disk drive unit and show a magnetic disk 101 mounted on a spindle motor 102 for spinning the disk 101. A voice coil motor arm 104 carries a head gimbal assembly (HGA) 100 that includes a micro-actuator 105 with a slider 103 incorporating a read/write head. A voice-coil motor (VCM) is provided for controlling the motion of the motor arm 104 and, in turn, controlling the slider 103 to move from track to track across the surface of the disk 101, thereby enabling the read/write head to read data from or write data to the disk 101. In operation, a lift force is generated by the aerodynamic interaction between the slider 103, incorporating the read/write transducer, and the spinning magnetic disk 101. The lift force is opposed by equal and opposite spring forces applied by a suspension of the HGA 100 such that a predetermined flying height above the surface of the spinning disk 101 is maintained over a full radial stroke of the motor arm 104.
FIG. 2 illustrates the head gimbal assembly (HGA) 100 of the conventional disk drive device of FIG. 1 incorporating a dual-stage actuator. However, because of the inherent tolerances of the VCM and the head suspension assembly, the slider 103 cannot achieve quick and fine position control which adversely impacts the ability of the read/write head to accurately read data from and write data to the disk. As a result, a PZT micro-actuator 105, as described above, is provided in order to improve the positional control of the slider and the read/write head. More particularly, the PZT micro-actuator 105 corrects the displacement of the slider 103 on a much smaller scale, as compared to the VCM, in order to compensate for the resonance tolerance of the VCM and/or head suspension assembly. The micro-actuator 105 enables, for example, the use of a smaller recording track pitch, and can increase the “tracks-per-inch” (TPI) value by 50% for the disk drive unit, as well as provide an advantageous reduction in the head seeking and settling time. Thus, the PZT micro-actuator 105 enables the disk drive device to have a significant increase in the surface recording density of the information storage disks used therein.
As shown in FIG. 2, the HGA 100 includes a suspension 106 having a flexure 108. The flexure 108 provides a suspension tongue 110 to load the PZT micro-actuator 105 and the slider 103. Two outwardly protruding traces 112, 114 are provided to the flexure 108 on opposite sides of the suspension tongue 110. Each of the traces 112, 114 has one end portion connected with a float plate 116 and another end portion connected with multi traces 118 that are electrically connected to bonding pads 120.
Referring to FIG. 3, a conventional PZT micro-actuator 105 includes a metal frame 130 which has a top support 132, a bottom support 134, and two side arms 136, 138 that interconnect the two supports 132 and 134. The side arms 136, 138 each have a PZT element 140, 142 attached thereto. The slider 103 is supported on the top support 132.
Referring to FIG. 4, the PZT micro-actuator 105 is physically coupled to the suspension tongue 110 by the bottom support 134 of the frame 130. The bottom support 134 may be mounted on the suspension tongue 110 by epoxy or laser welding, for example. Three electrical connection balls 150 (gold ball bonding or solder ball bonding, GBB or SBB) are provided to couple the PZT micro-actuator 105 to the suspension traces 118 located at the side of each PZT element 140, 142. In addition, there are four metal balls 152 (GBB or SBB) for coupling the slider 103 to the traces 118 for electrical connection of the read/write transducers. When power is supplied through the suspension traces 118, the PZT elements 140, 142 expand or contract to cause the two side arms 136, 138 to bend in a common lateral direction. The bending causes a shear deformation of the frame 130, e.g., the rectangular shape of the frame becomes approximately a parallelogram, which causes movement of the top support 132. This causes movement of the slider 103 connected thereto, thereby making the slider 103 move on the track of the disk in order to fine tune the position of the read/write head. In this manner, controlled displacement of slider 103 can be achieved for fine positional tuning.
FIG. 5 illustrates how the PZT micro-actuator 105 works when a voltage is applied to the PZT elements 140, 142. For example, when a positive sine voltage is input to the PZT element 140 of the micro-actuator which has a positive polarization, in the first half period, the PZT element 140 will shrink and cause the side arm 136 to deform as a water waveform shape. Since the slider 103 is mounted on the top support 132, this deformation will cause the slider to move or sway towards the left side. Likewise, when a negative sine voltage is input to the PZT element 142 of the micro-actuator which has a positive polarization, in the second half period, the PZT element 142 will shrink and cause the side arm 138 to deform as a water waveform shape. This deformation will cause the slider 103 to move or sway towards the right side. Of course, this operation may depend on the electric control circle and PZT element polarization direction, but the work principle is well known.
Because the PZT micro-actuator 105 moves in a sway-like manner, a suspension resonance is generated when the PZT micro-actuator 105 is operated. The suspension resonance limits the performance characteristics of the disk drive device.
For example, FIG. 6 illustrates testing data of the resonance of a prior PZT micro-actuator design. As illustrated, when the PZT micro-actuator is operated (exciting the PZT), a suspension resonance is generated due the relatively large reaction force of the suspension. The curve 160 illustrates a resonance when the suspension base plate is shaken or excited, and the curve 170 illustrates a resonance when the PZT element of the micro-actuator is excited.
Also, because the PZT element used for the micro-actuator is constructed of ceramic, the brittleness of the ceramic material will generate ceramic particles as the PZT element is continuously deformed backwards and forwards when a voltage is applied. Particles inside of the disk drive device can cause serious damage to the magnetic head and/or disk, and therefore, particle control is very tight and a particle free design is needed.
Due to limitations of ceramic PZT properties, a relatively high voltage or a multi-layer PZT element has to be used in order to achieve a target displacement to move the slider. However, a relatively high voltage is difficult for the control system of the disk drive device to complete and power consumption is big. A multi-layer PZT element will increase the mass of the micro-actuator. These drawbacks will effect the head static and dynamic performance, e.g., such as shock performance.
Additionally, a multi-layer ceramic PZT element is relatively expensive to manufacture. Thus, in order to achieve a lower cost, an improved structure for the micro-actuator is needed.
Thus, there is a need for an improved system that does not suffer from the above-mentioned drawbacks.